Fully biodegradable mulching film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of degradable mulching films, and relates to a fully biodegradable mulching film as well as a preparation method and application thereof, and the fully biodegradable mulching film is prepared from oxidized starch, sodium carboxymethyl cellulose, polyvinyl alcohol and a plasticizer; the adhesive comprises the following components in parts by weight: 15-25 parts of oxidized starch, 20-25 parts of sodium carboxymethyl cellulose, 12-20 parts of polyvinyl alcohol and 30-40 parts of a plasticizer. The oxidized starch is prepared from cassava starch. The full-biodegradable mulching film is obtained by compounding polymer materials, the raw materials in the formula are low in price, can come from agricultural wastes, do not generate micro-plastics in the degradation process, and can be fully biodegraded, so that the problem of environmental pollution caused by the mulching film is solved, and the sustainable development of agriculture is promoted; the antibacterial activity on escherichia coli is realized; the preparation process is simple and safe, only water bath operation is needed, and operation such as professional production line and pressurization is not needed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of degradable mulching film, and relates to a full-biodegradable mulching film and a preparation method and application thereof. BACKGROUND

[0002] With the development of modern agriculture, mulching film can increase temperature, conserve soil moisture, and improve the growth environment of crops, and is widely used in China. China has become the largest country in the world for mulching film planting. Mulching film can inhibit weed growth, reduce evaporation and soil latent heat loss, and increase light uniformity, thereby creating good conditions for plant root development and improving crop yield. In 2019, the amount of agricultural plastic film used in China was 2.408 million tons, and the amount of mulching film used increased by 15% per year. In 2022, the cumulative output of the agricultural film industry in China increased by 4.1% compared with the previous year. However, the large amount of film used has caused problems of waste recycling and environmental pollution. Residual film pollutes the soil and affects crop growth, seriously threatening the sustainable development of agriculture in China.

[0003] Most of the current mulching film is made of polyethylene, which is difficult to degrade naturally and remains in the soil, hindering air and water permeability, affecting crop root extension and nutrient absorption, causing resource waste, and damaging the ecological environment, which seriously threatens the sustainable development of agriculture. More importantly, plastic particles formed by the fragmentation of residual film can adsorb heavy metal ions and organic pollutants, making soil remediation more difficult. These microplastics can also enter the food chain and cause ecological chain reactions. Burning residual film in the field releases harmful chemicals, pollutes the atmosphere, and harms plant growth, causing secondary pollution. Therefore, the development and promotion of degradable mulching film is a key measure to balance agricultural yield and ecological protection.

[0004] To address the pollution and harm caused by plastic mulching film, China has introduced a series of policies to promote the research and development and promotion of degradable mulching film, such as the "Opinions on Further Strengthening Plastic Pollution Control" and the "14th Five-Year Plan for Plastic Pollution Control Action Plan", which require comprehensive and in-depth solutions to agricultural film pollution problems and the development and promotion of degradable mulching film to achieve green and sustainable agricultural development. SUMMARY

[0005] The main purpose of the present application is to overcome the defects in the prior art and provide a full-biodegradable mulching film and a preparation method and application thereof.

[0006] To achieve the above-mentioned purpose, the specific technical solutions are as follows: The present application provides a full-biodegradable mulching film prepared from oxidized starch, sodium carboxymethyl cellulose, polyvinyl alcohol, and plasticizer; Said oxidized starch 15-25 parts by weight, sodium carboxymethyl cellulose 20-25 parts, polyvinyl alcohol 12-20 parts, plasticizer 30-40 parts by weight; Said oxidized starch is prepared from cassava starch.

[0007] The present application obtains the full biodegradable mulch film by compounding polymer materials, the formula raw material price is low, said sodium carboxymethyl cellulose is prepared from agricultural wastes such as bamboo shoot shell straw, and has good adhesion, can be combined with cellulose, starch and the like, is transparent after drying, forms a film, the film has strong folding resistance, good airtightness and certain water resistance; polyvinyl alcohol has good water solubility, viscosity and stability, can be used as an adhesive, an emulsifier and a dispersant, has excellent film-forming property, and can significantly improve the tensile strength of the mulch film; the oxidized starch prepared from cassava starch has low gelatinization temperature (not more than 60 DEG C), more stable paste, is green and degradable, and has excellent freeze-thaw stability.

[0008] The full biodegradable mulch film of the present application does not produce microplastics during the degradation process, is fully biodegradable, and solves the environmental pollution problem caused by the mulch film; and has antibacterial property on escherichia coli.

[0009] Preferably, said full biodegradable mulch film, by weight, said oxidized starch 20 parts, sodium carboxymethyl cellulose 20 parts, polyvinyl alcohol 12 parts, plasticizer 30 parts.

[0010] Further, the method for preparing said oxidized starch from cassava starch comprises the following steps: A1 the cassava starch is mixed with water to prepare a 35-45% concentration starch milk; A2 the pH of the starch milk is adjusted to 8-10 by using sodium hydroxide solution, so that the emulsion reaction process is kept alkaline, sodium hypochlorite solution is slowly and continuously added, the temperature is 40-50 DEG C, and the reaction is continued until the pH remains basically unchanged; A3 after the reaction is completed, 14-16% sodium sulfite solution is used to reduce the residual sodium hypochlorite in the starch milk, dilute hydrochloric acid is used for neutralization until the pH is 6.5-7.5, the starch milk is washed and filtered with distilled water for multiple times until no Cl is detected by silver nitrate test, and finally the oxidized starch is obtained by drying, crushing and sieving. -

[0011] Further, the percentage of chlorine in said sodium hypochlorite added to the absolute dry cassava starch is 2-4%.

[0012] Further, said sodium carboxymethyl cellulose is prepared by using bamboo shoot shell as raw material, refining cellulose by chemical degumming process, and using organic solvent ethanol as reaction medium to prepare sodium carboxymethyl cellulose by solvent method.

[0013] ​Specifically, the preparation method of the sodium carboxymethyl cellulose comprises the following steps: B1 raw material pretreatment: taking bamboo shoot shells, after washing, drying and crushing, bamboo shoot shell powder is obtained; B2 chemical degumming refined cellulose: the bamboo shoot shell powder is sequentially subjected to alkali degumming, neutralization treatment and bleaching to obtain refined cellulose; the alkali degumming uses sodium hydroxide solution as a degumming agent, and the bleaching uses hydrogen peroxide as a bleaching agent; B3 solvent method for preparing sodium carboxymethyl cellulose: taking ethanol as a reaction medium, the refined cellulose is sequentially subjected to alkalization reaction, etherification reaction, neutralization washing and drying and crushing to obtain a sodium carboxymethyl cellulose product.

[0014] Further, in step B3, the etherification reaction uses chloroacetic acid as an etherification agent.

[0015] Further, the plasticizer is glycerol.

[0016] As a plasticizer, glycerol can be inserted between high molecular chains to reduce intermolecular forces and improve the flexibility and ductility of the mulch film, thereby preventing the mulch film from being broken during use.

[0017] The application also provides a preparation method of the above-mentioned fully biodegradable mulch film, comprising the following steps: (1) uniformly coating solid paraffin on an iron plate or a stainless steel tray with smooth and dry surface; (2) heating 2000-4000 parts of distilled water, and adding sodium carboxymethyl cellulose in multiple times to stir and dissolve; adding oxidized starch to stir until completely dissolved; adding polyvinyl alcohol and a plasticizer to stir until completely dissolved, to obtain a mixed solution; (3) sieving the mixed solution, uniformly pouring into the iron plate of step (1), and placing in a room temperature drying condition to naturally shape, and taking out to obtain the fully biodegradable mulch film.

[0018] The preparation process of the fully biodegradable mulch film is simple and safe, and does not need a professional production line and pressure operation.

[0019] Preferably, in step (3), the liquid formed after the mixed solution is poured into the iron plate or the stainless steel tray has a thickness of 0.4-0.6 cm, preferably 0.5 cm.

[0020] Further, the water content of the fully biodegradable mulch film is 6-8%.

[0021] Further, in step (2), the heating temperature of the distilled water is 50-60℃.

[0022] Heating the distilled water to 50-60℃ is beneficial / conducive to the more stable gelatinization of the oxidized starch.

[0023] Further, in step (2), the water heating method is water bath heating.

[0024] Preferably, in step (2), the sodium carboxymethyl cellulose is added in multiple times, and after stirring and dissolving, the oxidized starch is added, and finally the polyvinyl alcohol and plasticizer are added.

[0025] Further, in step (2), the stirring speed when adding the sodium carboxymethyl cellulose is 2000-4000 r / min, and the stirring time is 5-20 min; the stirring speed when adding the oxidized starch, polyvinyl alcohol and plasticizer is 2000-4000 r / min.

[0026] Further, in step (3), the mixed solution is passed through a 16-mesh sieve.

[0027] Preferably, in step (3), the relative humidity is 50%-60%.

[0028] The application further provides the application of the above-mentioned fully biodegradable mulching film in the field of agricultural product planting.

[0029] Compared with the prior art, the application has the following remarkable beneficial effects: The application obtains the fully biodegradable mulching film by compounding polymer materials, the formula raw material is low in price, the sodium carboxymethyl cellulose is prepared from agricultural wastes such as bamboo shoot shell and straw, no microplastics are generated in the degradation process, the film can be fully biodegradable, the environmental pollution problem caused by the film is solved, and the sustainable development of agriculture is promoted; the film has bacteriostatic property on escherichia coli; and the preparation process is simple and safe, only water bath operation is needed, and no professional production line and pressure operation are needed. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0031] Figure 1 is the bacteriostatic rate diagram of the mulching film of the example and the comparative example of the application.

[0032] Figure 2 is the static contact angle diagram of the mulching film of the example and the comparative example of the application.

[0033] Figure 3 is the water solubility diagram of the mulching film of the example and the comparative example of the application. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0035] Unless otherwise specified, the technical or conditions in the embodiments of the present application are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. Unless otherwise specified, the reagents or instruments used are all conventional products that can be purchased through a regular channel.

[0036] The preparation of oxidized starch includes the following steps: A1The cassava starch is mixed with water to prepare a starch milk with a concentration of 40%; A2The pH of the starch milk is adjusted to 9 by using a sodium hydroxide solution, so that the emulsion reaction process is kept alkaline. A sodium hypochlorite solution is slowly and continuously added, and the temperature is 45℃. The reaction is continued until the pH basically remains unchanged. A3After the reaction is completed, a 15% sodium sulfite solution is used to reduce the residual sodium hypochlorite in the starch milk. Then, dilute hydrochloric acid is used for neutralization until the pH is 7. After multiple washing and filtering with distilled water, the washing liquid is tested for Cl- by using silver nitrate until no Cl- is detected. Finally, the oxidized starch is obtained by drying, crushing and sieving. -

[0037] The preparation of sodium carboxymethyl cellulose includes the following steps: B1Raw material pretreatment: The shell of bamboo shoots is cleaned, dried and crushed to obtain bamboo shoot shell powder; B2Chemical degumming and refining of cellulose: 10g of the bamboo shoot shell powder is pre-hydrolyzed with dilute sulfuric acid, and then 30g / L of a sodium hydroxide solution is prepared and boiled for 1h. After cooling to room temperature, the alkali impurities are washed away with distilled water and then dried. Then, 3% of H2O2 is added for bleaching for 0.5h. After filtering and washing to neutral, the white bamboo shoot shell fiber is dried in a drying oven at 60℃ until the weight is constant. B3Preparation of sodium carboxymethyl cellulose by solvent method: 5g of the refined bamboo shoot shell cellulose is alkalinized by adding 15% of a sodium hydroxide ethanol solution at 25℃ for 1.5h. Then, 2.5g of chloroacetic acid is dissolved in the ethanol solution, and then etherification reaction is carried out at 70℃ for 4.5h. After the etherification reaction, the solution is cooled to room temperature, and the pH is adjusted to 7.0 by adding a 5% hydrochloric acid solution dropwise. After filtering, the filter cake is washed with a 75% ethanol solution until the washing liquid is free of Cl-. Then, the product is dried at 65℃ under vacuum until the weight is constant. After crushing and sieving through an 80-mesh sieve, the sodium carboxymethyl cellulose product is obtained.

[0038] The above-mentioned substances are used in the following embodiments.​

[0039] Example 1 Preparation of a fully biodegradable mulch film: (1) Take 20 parts of oxidized starch, 20 parts of sodium carboxymethyl cellulose, 20 parts of polyvinyl alcohol, 35 parts of glycerol, and 3000 parts of distilled water by weight; (2) Uniformly coat solid paraffin on an iron tray; (3) Heat the distilled water to a constant temperature under the condition of a water bath at 80°C, add sodium carboxymethyl cellulose in three times, stir with a stirrer at 3000 r / min for 10 min, add oxidized starch, stir with a high-speed stirrer at 3000 r / min until completely dissolved, and add polyvinyl alcohol and glycerol and stir thoroughly until completely dissolved; (4) Pass the prepared solution through a 16-mesh sieve, uniformly pour it into the iron tray of step (2), place it in a room temperature drying condition, and naturally set. It can be taken off with a tool to obtain a fully biodegradable mulch film (CM1) with a thickness of 1.4 mm.

[0040] Example 2: Preparation of a fully biodegradable mulch film: (1) Take 20 parts of oxidized starch, 20 parts of sodium carboxymethyl cellulose, 20 parts of polyvinyl alcohol, 35 parts of glycerol, and 3000 parts of distilled water by weight; (2) Uniformly coat solid paraffin on an iron tray; (3) Heat the distilled water to a constant temperature under the condition of a water bath at 80°C, add sodium carboxymethyl cellulose in three times, stir with a stirrer at 3000 r / min for 10 min, add oxidized starch, stir with a high-speed stirrer at 3000 r / min until completely dissolved, and add polyvinyl alcohol and glycerol and stir thoroughly until completely dissolved; (4) Pass the prepared solution through a 16-mesh sieve, uniformly pour it into the iron tray of step (2), place it in a room temperature drying condition, and naturally set. It can be taken off with a tool to obtain a fully biodegradable mulch film (CM1) with a thickness of 1.4 mm.

[0041] Example 3 (1) Take 20 parts of oxidized starch, 20 parts of sodium carboxymethyl cellulose, 20 parts of polyvinyl alcohol, 35 parts of glycerol, and 3000 parts of distilled water by weight; (2) Uniformly coat solid paraffin on an iron tray; (3) Heat the distilled water to a constant temperature under the condition of a water bath at 80°C, add sodium carboxymethyl cellulose in three times, stir with a stirrer at 3000 r / min for 10 min, add oxidized starch, stir with a high-speed stirrer at 3000 r / min until completely dissolved, and add polyvinyl alcohol and glycerol and stir thoroughly until completely dissolved; (4) The prepared solution was passed through a 16-mesh sieve and uniformly poured into the iron pan of step (2), placed in a room temperature drying condition, and naturally shaped. The film with a thickness of 1.4 mm (CM3) was obtained by taking it out with a tool.

[0042] Example 4 (1) 20 parts of oxidized starch, 23 parts of sodium carboxymethyl cellulose, 17 parts of polyvinyl alcohol, 30 parts of glycerol, and 3000 parts of distilled water were weighed according to the proportion; (2) Solid paraffin was uniformly coated on the iron pan; (3) The distilled water was heated to a constant temperature under the condition of a water bath at 80°C. The sodium carboxymethyl cellulose was added in three times and stirred at 3000 r / min for 10 min with a stirrer. The oxidized starch was added and stirred at 3000 r / min with a high-speed stirrer until completely dissolved. The polyvinyl alcohol and glycerol were added and stirred until completely dissolved; (4) The prepared solution was passed through a 16-mesh sieve and uniformly poured into the iron pan of step (2), placed in a room temperature drying condition, and naturally shaped. The film with a thickness of 1.4 mm (CM4) was obtained by taking it out with a tool.

[0043] Comparative Example 1 Commercial polyethylene mulch film (PE): The polyethylene mulch film was a mulch film with a material of polyethylene (PE) produced by Shandong Wanchen Plastic Technology Co., Ltd.

[0044] Comparative Example 2 Commercially available degradable mulch film (JLM): The degradable mulch film was a degradable mulch film with a material of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) produced by Zhejiang Jiale Honey Company.

[0045] The mulch films in the examples and comparative examples were tested, and single factor analysis of variance (ANOVA) was performed using SPSS with a significance level p < 0.05.

[0046] Tensile property: According to "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets" (GB / T1040.3-2006), the sample was cut into a 1x10 cm strip film, and after being baked in a constant temperature drying oven at 40°C for 2 h, uniaxial tension was performed on a tensile testing machine at a speed of 50 mm / min, with at least 3 times for each group. The tensile strength and elongation at break were calculated according to the following formulas: , ; In the formula: F m is the maximum tensile stress of the sample (N); W is the width of the sample (mm); T is the thickness of the sample (mm); Lb L1 represents the length of the specimen at which fracture occurs (mm); L2 represents the initial length of the specimen (mm).

[0047] The tensile strength and elongation results are shown in Table 1: Table 1. Results of Tensile Strength and Elongation

[0048] Antibacterial properties: Two × 2 cm samples of plastic film were placed in Erlenmeyer flasks containing 10¹⁰ E. coli bacterial suspension and incubated at 35℃ with shaking at 150 rpm for 24 h. 10 μl of the bacterial suspension was then spread onto nutrient agar plates and incubated for another 24 h. Colony counts were performed using the plate count method, with each type of plastic film sample repeated three times. The calculation formula is as follows: Antibacterial rate = (Antibacterial zone diameter - Sample diameter) / Sample diameter Inhibition zone method: Escherichia coli bacterial suspension was evenly spread on an agar plate. A 2cm diameter circular sample of mulch film was placed on the plate surface and incubated at 35℃ for 24 hours. The diameter of the inhibition zone formed around the sample was measured to evaluate the antibacterial effect of the mulch film. Each mulch film sample was repeated 3 times. The results are shown in Table 2. Table 2. Antibacterial Results of Mulch Film

[0049] like Figure 1 As shown in the figure, the antibacterial experiment showed that, except for PE and JLM, other plastic films had an inhibitory effect on Escherichia coli. The inhibition zone and antibacterial intensity of CM were significantly higher than those of PE and JLM (p<0.05), indicating that CM has the ability to inhibit the reproduction and spread of Escherichia coli.

[0050] Hydrophobicity: Place the plastic film sample to be tested flat on the test platform, and use a micro-syringe to drop distilled water onto the surface of the plastic film. After the water droplet stabilizes, immediately measure the contact angle. Measure each type of plastic film sample three times at different locations and calculate the average value.

[0051] like Figure 2 As shown, the static contact angle of the mulch film can measure its hydrophobicity. When the static contact angle is less than 90°, the solid surface is hydrophilic; otherwise, it is hydrophobic. The results show that the static contact angle of PE is 95.6°, JLM is 75.2°, and CM1 is 98.7°. Among them, JLM exhibits hydrophilicity, while PE and CM1 exhibit hydrophobicity. Good hydrophobicity can prevent water from penetrating the film, ensuring that irrigation or rainwater can be accurately retained on the soil surface for crop absorption, while also preventing the film surface from becoming wet and sticking together or breaking.

[0052] 1.3.2.2 Determination of the durability and degradability of plastic film; To measure the persistence by water solubility, 3 pieces of 2x2cm samples of each mulch film were cut, dried in a constant temperature oven at 100 DEG C for 24h to constant weight, weighed, soaked in distilled water for 24h, taken out, dried at 100 DEG C for 24h to constant weight, weighed, and the weight loss rate was calculated to represent the water solubility. In the formula, m0 is the mass (g) of the initial dried sample; m1 is the mass (g) of the dried sample after water soaking, and SW is the weight loss rate (%). The 2x2cm mulch film samples were buried in soil (temperature 20 DEG C, soil humidity 77%, pH 7.5), slightly compacted, and then placed in an incubator (temperature 19~21 DEG C) for incubation. On the 0th, 9th and 19th days, the samples were taken out, the adhered soil was removed as much as possible, and the surface morphological changes of the samples were observed to determine the degradability of the mulch film.

[0053] The degradable mulch film is measured by water solubility to determine the persistence, and too large water solubility will cause the mulch film to disintegrate prematurely, and too small water solubility will result in that the mulch film cannot be degraded for a long time. Figure 3 As shown in the formula, experiments show that the water solubility of different mulch films is significantly different, and the water solubility of CM1 mulch film is significantly higher than that of JLM mulch film.

[0054] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, and should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A fully biodegradable mulch film, characterized in that, It is prepared using oxidized starch, sodium carboxymethyl cellulose, polyvinyl alcohol, and plasticizer; By weight, the oxidized starch comprises 15-25 parts, sodium carboxymethyl cellulose 20-25 parts, polyvinyl alcohol 12-20 parts, and plasticizer 30-40 parts; The oxidized starch is prepared from cassava starch.

2. The fully biodegradable mulch film according to claim 1, characterized in that, The ingredients, by weight, are 20 parts oxidized starch, 20 parts sodium carboxymethyl cellulose, 12 parts polyvinyl alcohol, and 30 parts plasticizer.

3. The fully biodegradable mulch film according to claim 1 or 2, characterized in that, The plasticizer is glycerol.

4. A method for preparing a fully biodegradable mulch film as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Apply solid paraffin wax evenly to an iron pan or stainless steel tray; (2) Heat 2000-4000 parts of distilled water, add sodium carboxymethyl cellulose in several batches and stir to dissolve; add oxidized starch, polyvinyl alcohol and plasticizer and stir well to obtain a mixed solution; (3) Sieve the mixed solution and pour it into the iron pan or stainless steel tray of step (1). Place it under room temperature and dry conditions to set naturally. Take it out to obtain the fully biodegradable mulch film.

5. The method for preparing the fully biodegradable mulch film according to claim 4, characterized in that, In step (2), the distilled water is heated to 50-60℃.

6. The method for preparing the fully biodegradable mulch film according to claim 4, characterized in that, In step (2), the stirring speed when adding sodium carboxymethyl cellulose is 2000-4000 r / min and the stirring time is 5-20 min.

7. The method for preparing the fully biodegradable mulch film according to claim 6, characterized in that, In step (2), the stirring speed for adding oxidized starch, polyvinyl alcohol and plasticizer is 2000-4000 r / min.

8. The method for preparing the fully biodegradable mulch film according to claim 6 or 7, characterized in that, In step (3), the mixed solution is passed through a 16-mesh sieve.

9. The method for preparing the fully biodegradable mulch film according to claim 1, characterized in that, In step (3), the liquid thickness formed after the mixed solution is poured into the iron pan or stainless steel tray is 0.4-0.6cm, preferably 0.5cm.

10. The application of the fully biodegradable mulch film as described in any one of claims 1-5 in the field of agricultural product cultivation.

Images